How many drops does Medina Lake have left?

As the water level in Medina Lake continues to drop, such long-submerged items as this boat and automobile are being exposed.

Photo By William Luther/San Antonio Express-News

USGS officials measure the distance to the bottom of Medina Lake at the base of the dam in an attempt to determine how much water remains in the lake.

Photo By Harry Thomas

Scroll down for a larger version of this graphic.

Photo By William Luther/San Antonio Express-News

Trash lines the shore of Medina Lake Thursday Nov. 29, 2012 next to the spillway side of the dam.

Photo By William Luther/San Antonio Express-News

USGS officials measure the bottom of Medina Lake Thursday Nov. 29, 2012 at the base of the dam in an effort to better measure how much water remains in the lake, which was 10.93 percent full on Thursday according to the Texas Water Deelopment Board website www.waterdatafortexas.org. As of Thursday the lake was 68.99 feet below conservation pool.

Photo By William Luther/San Antonio Express-News

A fence line sits high and dry Thursday Nov. 29, 2012 on a section of the Media Lake lakebed that hasn't been above the water in at least 50 years. As of Thursday the lake was 68.99 feet below conservation pool, or 10.93 percent full according to the Texas Water Development Board website www.waterdatafortexas.org.

Photo By William Luther/San Antonio Express-News

A still-under-construction home is seen on Medina Lake Thursday Nov. 29, 2012. As of Thursday the lake was 68.99 feet below conservation pool, or 10.93 percent full according to the Texas Water Development Board website www.waterdatafortexas.org.

Photo By William Luther/San Antonio Express-News

USGS officials measure the bottom of Medina Lake Thursday Nov. 29, 2012 at the base of the dam in an effort to better measure how much water remains in the lake, which was 10.93 percent full on Thursday according to the Texas Water Deelopment Board website www.waterdatafortexas.org. As of Thursday the lake was 68.99 feet below conservation pool.

Photo By William Luther/San Antonio Express-News

Medina Lake is seen Wednesday Aug. 29, 2012. The Texas Water Development Board reported Wednesday, via its website, the lake is 13.88 percent full and is 63.34 feet below normal pool elevation.

Photo By William Luther/San Antonio Express-News

A back hoe stands on top of Medina Lake dam Wednesday Aug. 29, 2012. The Texas Water Development Board reported Wednesday, via its website, the lake is 13.88 percent full and is 63.34 feet below normal pool elevation.

Photo By William Luther/San Antonio Express-News

Boat docks once floating over deep water are stranded high and dry Wednesday Aug. 29, 2012 on Medina Lake. The Texas Water Development Board reported Wednesday, via its website, the lake is 13.88 percent full and is 63.34 feet below normal pool elevation.

Photo By William Luther/San Antonio Express-News

Medina Lake is seen Wednesday Aug. 29, 2012. The Texas Water Development Board reported Wednesday, via its website, the lake is 13.88 percent full and is 63.34 feet below normal pool elevation.

Photo By William Luther/San Antonio Express-News

6. Heavy rains early in the year relieve the drought temporarily, but Medina Lake continues to dry up.

Photo By William Luther/San Antonio Express-News

Boat docks once floating over deep water are stranded high and dry Wednesday Aug. 29, 2012 on Medina Lake. The Texas Water Development Board reported Wednesday, via its website, the lake is 13.88 percent full and is 63.34 feet below normal pool elevation.

Photo By BOB OWEN/Express-News

A flood gauge can be seen, right, in the overflow spillway of Medina Lake, Monday, July 2, 2012.

Photo By William Luther/San Antonio Express-News

Medina Lake is seen in Wednesday Aug. 1, 2012.

Photo By William Luther/San Antonio Express-News

A long-dead, normally-submerged tree on what is the Medina Lake lakebed is seen Thursday Aug. 2, 2012 surrounded by grass land. The Texas Water Development Board's website reports the lake is 59.59 feet low and is currently only 16.09 percent full.

Photo By William Luther/San Antonio Express-News

Dead trees, seen in Thursday Aug. 2, 2012, normally covered by dozens of feet of Medina Lake water stand behind an electric fence a local rancher has erected on the dry lake bottom to graze livestock. The Texas Water Development Board's website reports the lake is 59.59 feet low and is currently only 16.09 percent full.

Photo By William Luther/San Antonio Express-News

A giant sink hole in Medina Lake is seen in Thursday Aug. 2, 2012 on the dry lake bed in front of the Holiday Villages community. The Texas Water Development Board's website reports the lake is 59.59 feet low and is currently only 16.09 percent full. Holiday Villages sales representative C.R. Edwards says the sink hole is called Jacobs Well by locals and is thought to connect to the aquifer.

Photo By William Luther/San Antonio Express-News

Much of Medina Lake, seen Thursday Aug. 2, 2012 from the bottom of the dry lake bed, has been dry so long local ranchers have erected fences to graze livestock. The Texas Water Development Board's website reports the lake is 59.59 feet low and is currently only 16.09 percent full

Photo By William Luther/San Antonio Express-News

A giant sink hole in Medina Lake is seen in Thursday Aug. 2, 2012 on the dry lake bed in front of the Holiday Villages community. The Texas Water Development Board's website reports the lake is 59.59 feet low and is currently only 16.09 percent full. Holiday Villages sales representative C.R. Edwards says the sink hole is called Jacobs Well by locals and is thought to connect to the aquifer.

Photo By William Luther/San Antonio Express-News

Medina Lake is seen in Wednesday Aug. 1, 2012 aerial images. The Texas Water Development Board's website reports the lake is 59.39 feet low and is currently only 16.22 percent full

Photo By William Luther/San Antonio Express-News

EDS NOTE: CAPTIONS TO BE UPDATED -- WILLIAM Medina Lake is seen in Wednesday Aug. 1, 2012 aerial images. The Texas Water Development Board's website reports the lake is 59.39 feet low and is currently only 16.22 percent full

Photo By William Luther/San Antonio Express-News

EDS NOTE: CAPTIONS TO BE UPDATED -- WILLIAM Medina Lake is seen in Wednesday Aug. 1, 2012 aerial images. The Texas Water Development Board's website reports the lake is 59.39 feet low and is currently only 16.22 percent full

Photo By William Luther/San Antonio Express-News

EDS NOTE: CAPTIONS TO BE UPDATED -- WILLIAM Medina Lake is seen in Wednesday Aug. 1, 2012 aerial images. The Texas Water Development Board's website reports the lake is 59.39 feet low and is currently only 16.22 percent full

Photo By William Luther/San Antonio Express-News

EDS NOTE: CAPTIONS TO BE UPDATED -- WILLIAM Medina Lake is seen in Wednesday Aug. 1, 2012 aerial images. The Texas Water Development Board's website reports the lake is 59.39 feet low and is currently only 16.22 percent full

Photo By William Luther/San Antonio Express-News

The island in Medina Lake is seen in a Wednesday Aug. 1, 2012 aerial image. The Texas Water Development Board's website reports the lake is 59.39 feet low and is currently only 16.22 percent full. At normal pool elevation the lake's water line rises all the way to the trees on the island.

Photo By Tom Reel/San Antonio Express-News

Boats are contained to a much smaller water area near the Red Cove Marina as Medina Lake water levels get very low and the real estate market is affected. July 6, 2012.

Photo By Tom Reel/San Antonio Express-News

Water front homes get farther away from the water as the Medina Lake water levels get very low and the real estate market is affected. July 6, 2012.

Photo By Tom Reel/San Antonio Express-News

Water front homes get farther away from the water as the Medina Lake water levels get very low and the real estate market is affected. July 6, 2012.

Photo By Tom Reel/San Antonio Express-News

Medina Lake water levels get very low and the real estate market is affected. July 6, 2012.

Photo By Tom Reel/San Antonio Express-News

Medina Lake water levels get very low and the real estate market is affected. July 6, 2012.

Photo By Tom Reel/San Antonio Express-News

Visitors try to make the best of low water at the county park as Medina Lake water levels get very low and the real estate market is affected. July 6, 2012.

Photo By JOHN DAVENPORT/SAN ANTONIO EXPRESS-NEWS

A sailboat lists on its side on the ground next to a beached dock Thursday January 19, 2012 as water levels at Medina Lake continue to plummet. The lake is 52 feet below pool and is expected to continue to drop as long as the long term forecast calls for below average rainfall. Because the lake is so low, farmers will only be able to draw water in March and April. John Davenport/San Antonio Express-News

Photo By JOHN DAVENPORT/SAN ANTONIO EXPRESS-NEWS

A dock that once floated in Medina Lake hangs on the side of the rocky bank by wires. The lake is 52 feet below pool and is expected to continue to drop. Because the lake is so low, farmers will only be able to draw water in March and April. The Bexar-Medina-Atascosa Counties Water Improvement District, which owns and operates the lake's dam has promised there will be enough water to meet its contract with San Antonio through 2012. John Davenport/San Antonio Express-News

More Information

Ghostly white fence posts and dead cypress trees that have not seen the sun in half a century are emerging from the vanishing Medina Lake.

With the lake now below 11 percent of its estimated storage capacity, each exposed post and trunk raise the threat that local residents will run out of water, farmers will have to let land go fallow and San Antonio will lose part of its water supply.

Based on the lake's current rate of decline, the water supply gates on the Medina Lake Dam will be exposed by the end of June, and the lake will be in effect empty, unless substantial rains fall.

But none of this is a precise calculation.

As the lake drops, how the rate of decline will change is unknown. So is the total amount of water there now.

“There is too much information here that we don't have,” said Larry Thomas, data chief for the San Antonio office of the U.S. Geological Survey.

On Thursday Thomas and a team of USGS hydrologists headed out on Medina Lake to map the bottom of it near the dam, check the accuracy of the lake's elevation gauge and resurvey the exact elevation of the dam.

The original brass markers on the 100-year-old-dam list its elevation as 7.81 feet higher that it actually is. Ever since this was made known in 1960s, data collected from the lake has had to be adjusted to meet the USGS' standard of elevation above sea level, according to USGS records.

A thorough mapping of the lake bottom has not been done since the mid-1990s. Since then floods, including the record-setting one of 2002 that threatened to topple the dam, have dumped an unknown amount of sediment, reducing its storage capacity.

The USGS gauge on the dam will have to be lowered for the third time this year to keep it in contact with the ever-dropping lake.

It's that constant drop that has locals nervous.

The lake sits on top of porous limestone and has a direct influence on local wells.

At the north end of the lake, where there is no water left, wells started running dry last year, said Cappi Phillips, 73, who lives on the lake.

Some homes take their water directly from the lake via long pipes that run across the shoreline. With the lake down almost 70 feet, many of the homes are close to being left dry.

This is something Phillips expected, but has never seen. She's the daughter of Joe Granieri, who established Joe's Wharf in 1916 near the Medina Lake Dam.

“My dad used to always say it would fill up every 20 years and it would go dry every 20 years,” she said.

But for Phillips, the closest she ever came to seeing that was the drought of the 1950s. Now her boat ramp at Red Cove is the only one open to the public that provides access to deep water, and she is waiting and dreading the day it, too, goes dry.

Farmers already are preparing to go without irrigation water from Medina Lake. They received their last allotment of water from the lake at the start of the fall growing season.

For them, the storage capacity of the lake is paramount.

“It is uncharted territory for us,” said Brad Stull a vegetable farmer for Constanzo Farm in Atascosa County. “I've only been doing this for 17 years, but we've never had a year when there was no canal water.”

Stull estimates about half of the fields he works will have to be left fallow next year. He can't risk planting them with vegetables unless assured he can irrigate once a week.

What acreage Stulls will be able to farm will be irrigated by water from wells drilled into the Edwards Aquifer.

Stulls said those wells were drilled in the 1950s, which he is told is the last time there was no water available from Medina Lake.

The water left in Medina Lake now is promised by contract to the San Antonio Water System, which uses it as a secondary source to the aquifer.

Regardless if it takes the water or not, the public utility has to pay for it, and SAWS is trying to extend the supply for as long as possible, explained Chuck Ahrens, vice president of water resources and conservation at SAWS.

It's pulling about 400 acre-feet from the lake a month, enough to meet the demand of 14,400 households.

By stretching it out, Ahrens said, the utility buys time while it hopes for rain.